The aim of the study was to demonstrate the degeneration of the dopaninergic nigrostriatal pathway in Parkinsons disease(PD) and Essential Tremor (ET) by using the cocaine derivative 99mTc-TRODAT-1 SPECT and correlate the findings to the clinical severities (Hoehn and Yahr scale, H/Y). 28 patients with idiopathic Parkinsons disease, 10 patients with Essential Trenor and 19 healthy volunteers were investigated. The acquisition were performed 3 h postinjection of 99mTc-TRODAT-1, ROIs were drawn over the images of striatum and cerebellum, and ratios of striatum to cerebellar(ST/CB) were calculated. Ratios differed significantly between PD and controls, but ratios didnt show significant difference between ET patients and controls. A significant correlation didnt exist between ratios and clinical severities. Hemiparkinsons patients revealed significantly diminished 99mTc-TRODAT-1 binding not only clinically affected but unaffected side. Our findings indicated that 99mTc-TRODAT-1 SPECT is not only a reliable method to discriminate between PD and controls but also a useful tool for differential diagnosis in clinically unclear cases such as ET resembling PD.